Apple is reportedly investigating a move by a Texas-based patents holding firm that has served papers on a host of iOS developers, claiming they have infringed its patents relating to in-app purchasing.

The patents firm – known as Lodsys – claims that Apple and other app store operators such as Google and Microsoft are licensed to use the technology to provide in-app billing services, but that these licenses do not extent to third-party developers.

In letters sent out last week, Lodsys demanded payment from an unspecified number of developers for use of its in-app technology, threatening legal action for those that refused. According to The Guardian, a number of iOS developers referred the claims to Apple’s legal department, on the basis that they had built their apps using Apple’s developer toolkit. The report notes that Apple’s legal department is “actively investigating” the matter and will feedback to developers later this week.

Lodsys owns four patents it acquired from their inventor (Dan Abelow) in 2004. These relate to in-app purchasing, interactive online ads, online help and subscription renewals. The in-app purchasing patent is thought to have been first filed back in the 1990s.

Lodsys’ move to extract royalties from developers saw it roundly attacked by many bloggers and industry commentators. Florian Mueller, who has tracked patent disputes in the US and EU, wrote on his blog that “Lodsys is trying to abuse the patent system in a way that could ultimately destroy the entire mobile apps economy, which is not only thriving on its own but has been and continues to be a key factor in making new mobile devices so useful and popular.”

The patents firm claimed it subsequently became a victim of an “amazing amount of spam, death threats [and] hateful bile” and issued a lengthy blog post to explain its position.